JP2008079275A - Surface acoustic wave element, and surface acoustic wave device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave element in which an IDT electrode having electrode fingers formed by layering a plurality of conductor layers has improved durability by suppressing the occurrence of fracture or peeling, etc. in these conductor layers, and to provide a surface acoustic wave device mounted with the element. <P>SOLUTION: The surface acoustic wave element 1 includes the IDT electrode 11 having the electrode fingers 11a on a piezoelectric substrate 10. The electrode fingers 11a are formed by layering an intermediate layer 12 and an electrode layer 13 having a thermal expansion coefficient larger than that of the intermediate layer 12. The electrode finger 11a has a trapezoidal cross section becoming wider toward the piezoelectric substrate 10. An angle α<SB>1</SB>formed by a side face 1 of the intermediate layer 12 is larger than an angle β<SB>1</SB>formed by a side face of the electrode layer 13. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface acoustic wave element having an IDT electrode formed on a piezoelectric substrate and a surface acoustic wave device on which the surface acoustic wave element is mounted.

  2. Description of the Related Art Conventionally, a surface acoustic wave element in which an interdigital transducer electrode (Inter Digital Transducer: hereinafter simply referred to as an IDT electrode) is formed on a piezoelectric substrate is known. This IDT electrode can mutually convert an electric signal and a surface acoustic wave. In addition to the IDT electrode, the surface acoustic wave element also has a reflector electrode arranged at a position sandwiching the IDT electrode, and the surface acoustic wave excited by the IDT electrode can be multiple-reflected by the reflector electrodes on both sides to confine energy. it can.

  In a duplexer used for a mobile terminal device such as a cellular phone, conventionally, a dielectric filter has been mainly used. However, in recent years, a surface acoustic wave device equipped with a surface acoustic wave element capable of being reduced in size and weight can be used. A wave device is used. The input level of the surface acoustic wave device is expanded from the 10 mW level for the interstage filter of the mobile terminal device to the 1 to 3 W level required by the duplexer of the mobile terminal device. In response, it is spreading. For this reason, in the surface acoustic wave device used for the duplexer of the mobile terminal device, the demand for the input level increases as the use frequency band increases.

  On the other hand, in recent years, the operating frequency of surface acoustic wave elements has been increased from several hundred MHz to several GHz. The line width of the IDT electrode included in the surface acoustic wave element becomes thinner in inverse proportion to the frequency as the frequency increases. Specifically, in the 800 MHz band, the electrode line width of the IDT electrode is about 1 μm, whereas in the 1.9 GHz band, the electrode line width is about 0.5 μm. Therefore, the electrode finger formed in the comb shape of the IDT electrode is required to be finely processed as the frequency band becomes higher.

  As described above, due to the fact that the electrode line width of the IDT electrode has become narrower and the input level of the surface acoustic wave element included in the duplexer has increased, the withstand power of the surface acoustic wave element in the GHz band The service life is shortened by two orders of magnitude or more compared to a surface acoustic wave device in the 800 MHz band.

  Also, when surface acoustic waves are excited and received using a thin electrode finger of an IDT electrode corresponding to a high frequency, if the signal power applied to the surface acoustic wave device is increased, the surface acoustic wave device is driven by the surface acoustic wave. The main surface of the piezoelectric substrate is distorted, and internal stress is generated in the electrode fingers of the IDT electrode. The internal stress causes a stress migration phenomenon in the electrode finger, destroys the electrode finger, and deteriorates the IDT electrode.

  In addition, in order to relieve this internal stress, Al atoms in the electrode fingers formed of Al (aluminum) migrate, resulting in accumulation of vacancies at the Al crystal grain boundaries, resulting in voids. And a hillock is generated. For this reason, in the surface acoustic wave device, characteristic deterioration with respect to performance such as propagation and resonance of the surface acoustic wave and destruction of the electrode fingers occur.

  Accordingly, the surface acoustic wave element including the IDT electrode is required to have durability against application of high power as the application is diversified. Therefore, instead of conventional IDT electrodes having electrode fingers formed of a single layer of metal material of Al or Al alloy, development of IDT electrodes having electrode fingers with different materials laminated to increase durability has been developed. It is being advanced.

  For example, in Patent Document 1, as shown in FIG. 13 of the present application, a material such as Ti (titanium) is interposed between the Al electrode layer 113 and the piezoelectric substrate 110 for the purpose of suppressing the occurrence of stress migration of the IDT electrode 111. There has been proposed a structure in which the intermediate layer 112 formed in (1) is arranged and covered with a protective film (metal film) 114.

  Patent Document 2 discloses a structure of an IDT electrode in which a first metal layer and a second metal layer are stacked. The cross-sectional shape of the IDT electrode is a trapezoid whose lower surface near the piezoelectric substrate is wider than the upper surface.

  Patent Document 3 discloses a reflector electrode structure in which the material of the reflector electrode is a single metal layer and the cross-sectional shape thereof is a trapezoid.

Patent Document 4 discloses a structure of an IDT electrode in which a first metal layer having a trapezoidal cross section and a second metal layer having a rectangular cross section are overlaid.
JP 2001-217672 A JP 2001-168671 A JP-A-3-217109 International Publication No. 2003 / 058813A1 Pamphlet

  Incidentally, in the structure of the IDT electrode 111 in Patent Document 1, the side surfaces of the intermediate layer 112 and the electrode layer 113 are formed substantially perpendicular to the main surface 110 a of the piezoelectric substrate 110. In this case, when the protective film 114 is formed by a deposition method such as a vapor deposition method, the material for forming the protective film 114 is incident from a direction substantially perpendicular to the main surface 110a of the piezoelectric substrate 110. On the side surface of the electrode finger 111a, the protective film 114 is formed thin. For this reason, the protective film 114 deteriorates the coverage with respect to the side surface of the electrode finger 111a, and as a result, there is a possibility that stress migration such as breakage or peeling occurs.

  Patent Document 2 discloses an IDT electrode having two types of electrode layers made of different materials and having a trapezoidal cross-sectional shape. However, since the thermal expansion coefficients of the two types of electrode layers are different, the boundary surface between the electrode layers is disclosed. Shear stress is likely to occur.

  Patent Document 3 merely discloses an electrode structure of a reflector having a trapezoidal cross-sectional shape.

  Patent Document 4 cannot prevent breakage and peeling of each electrode layer as well as Patent Document 2 when shear stress occurs at the interface between the two electrode layers because the two types of electrode layers have different thermal expansion coefficients. .

  An object of the present invention is to provide an IDT electrode that can suppress the occurrence of breakage or peeling of these conductor layers, while being an electrode finger in which a plurality of conductor layers are laminated, and can improve durability. A surface acoustic wave device and a surface acoustic wave device including the same are provided.

  According to the surface acoustic wave element of the present invention, the electrode finger is formed by laminating a plurality of conductor layers including the first conductor layer and the second conductor layer made of a material different from the material of the first conductor layer. Is formed. The first conductor layer has a trapezoidal shape in which a cross-sectional shape in a plane orthogonal to the longitudinal direction of the electrode finger extends in a direction approaching the piezoelectric substrate, and the second conductor layer includes the electrode finger. The cross-sectional shape on the surface orthogonal to the longitudinal direction of the substrate has a trapezoidal shape that widens in a direction approaching the piezoelectric substrate. The angle formed between the side surface of the first conductor layer and the main surface of the piezoelectric substrate is different from the angle formed between the side surface of the second conductor layer and the main surface of the piezoelectric substrate.

  According to this configuration, the electrode finger is formed by laminating two conductor layers, and the first conductor layer (intermediate layer) formed on the main surface of the piezoelectric substrate and the first conductor layer are formed on the electrode finger. It is formed of a conductor layer with the formed second conductor layer (electrode layer). The first conductor layer and the second conductor layer included in the electrode finger are formed so that a cross section in a plane perpendicular to the longitudinal direction of the electrode finger approaches the main surface of the piezoelectric substrate. That is, each of the first conductor layer and the second conductor layer has a trapezoidal shape.

  Thereby, even if the material for forming the protective film formed on the electrode finger of the IDT electrode is incident from a direction substantially perpendicular to the main surface of the piezoelectric substrate, the protective film is sufficiently applied to the side surface of the electrode finger. It is formed with an appropriate thickness. Therefore, since the adhesion between the protective film and the conductor layer does not become low unlike when the protective film has been formed thin, the protective film can be prevented from being broken or peeled off. Durability can be increased.

  Since each conductor layer can individually have a trapezoidal shape with a different inclination angle, the protective film can be broken or peeled off even if the characteristics (for example, thermal expansion coefficient) of the material forming each conductor layer are different. Etc. can be further suppressed. Thereby, while forming an electrode finger with a plurality of conductor layers, breakage and peeling of a protective film can be controlled well and durability of a surface acoustic wave element can be improved.

  In the above description, an example of an electrode finger in which two conductor layers are laminated has been described. However, the present invention can be applied to an electrode finger in which three or more conductor layers are laminated.

  When the second conductor layer is formed of a material having a larger thermal expansion coefficient than that of the first conductor layer, an angle formed between a side surface of the first conductor layer and a main surface of the piezoelectric substrate. However, it is preferable that the angle is larger than the angle formed between the side surface of the second conductor layer and the main surface of the piezoelectric substrate.

  According to this configuration, since the thermal expansion coefficient of the first conductor layer is smaller than the thermal expansion coefficient of the second conductor layer, the width of the thermal expansion occurring in the first conductor layer is generated in the second conductor layer. It becomes smaller than the width of thermal expansion. Here, “the width of thermal expansion” represents the width of extension in a direction substantially perpendicular to the side surface of each conductor layer. In addition, since the angle of the side surface of the first conductor layer is formed larger than the angle of the side surface of the second conductor layer, the shear stress due to the difference in the thermal expansion width of each conductor layer forming the electrode finger ( shear stress) can be reduced. Therefore, the extension in the direction along the main surface of the piezoelectric substrate in the width of the thermal expansion of each conductor layer can reduce the difference compared to the case where the side surfaces of each conductor layer are formed at the same angle. .

  In addition, when the second conductor layer is formed of a material having a smaller thermal expansion coefficient than the first conductor layer, the side surface of the first conductor layer and the main surface of the piezoelectric substrate The angle formed may be smaller than the angle formed between the side surface of the second conductor layer and the main surface of the piezoelectric substrate. As a result, it is possible to improve the durability of the surface acoustic wave device because it is possible to satisfactorily suppress the occurrence of breakage or peeling of the protective film covering the surface of the electrode finger while forming the electrode finger with a plurality of conductor layers. it can.

  The first conductor layer is formed on and in contact with the main surface of the piezoelectric substrate, the second conductor layer is formed on the first conductor layer, and the first conductor layer includes the first conductor layer. Preferably, the width of the cross section facing the second conductor layer is formed larger than the width of the cross section of the second conductor layer facing the first conductor layer. According to this configuration, since the joining surface of the second conductor layer is formed smaller than the joining surface of the first conductor layer, from the side surface of the first conductor layer on the first conductor layer. A protective film can be laminated in a region (step portion) up to the side surface of the second conductor layer. Thereby, the expansion | extension by the thermal expansion of a 2nd conductor layer is suppressed by the protective film on a 1st conductor layer. Therefore, the shear stress generated at the boundary between the first conductor layer and the second conductor layer can be further suppressed.

  The electrode finger of the IDT electrode may be covered with a protective film. Thereby, peeling of each conductor layer which forms an electrode finger can be prevented.

  The protective film is preferably formed of a material having a smaller coefficient of thermal expansion than that of the conductor layer forming the electrode finger having the largest coefficient of thermal expansion. Thereby, the protective film can suppress the expansion | extension by the thermal expansion of a 1st conductor layer or a 2nd conductor layer.

  The protective film is formed only on the IDT electrode, and may contain at least one of Ti, Cr, Nb, Pd, Cu and Ni as a material.

  The surface acoustic wave device of the present invention is obtained by mounting the above-described surface acoustic wave element on a mounting substrate, and has a highly reliable IDT electrode as described above. Thereby, it can be expected that the lifetime of the surface acoustic wave device will be extended.

As described above, according to the present invention, the shear stress generated in the electrode finger of the IDT electrode can be reduced. As a result, the temperature characteristics of the surface acoustic wave element can be improved. Furthermore, the generation of hillocks and voids due to stress migration can be suppressed, the IDT electrode is less likely to be broken with respect to high input power, and the durability of the surface acoustic wave element can be improved.

  The above-described or further advantages, features, and effects of the present invention will be made clear by the following description of embodiments with reference to the accompanying drawings.

  FIG. 1 is a plan view of a ladder-type surface acoustic wave element according to an embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line AA when the surface acoustic wave element is mounted on a mounting substrate.

  The surface acoustic wave element 1 includes a piezoelectric substrate 10 and an IDT electrode 11 formed on the main surface 10 a of the piezoelectric substrate 10. Here, the “main surface 10a of the piezoelectric substrate 10” refers to a surface of the plate-like piezoelectric substrate 10 on which the IDT electrode 11 is formed.

  The surface acoustic wave element 1 has a reflector electrode (hereinafter also referred to as a reflector) 19 having a slit shape at a position sandwiching the IDT electrode 11 in the signal propagation direction (up and down direction in the drawing) of the IDT electrode 11. I have. By this reflector 19, the surface acoustic wave excited by the IDT electrode 11 can be subjected to multiple reflection, and the energy of the generated surface acoustic wave can be confined.

  Further, in the surface acoustic wave element 1, an annular electrode 16 is formed on the main surface 10 a of the piezoelectric substrate 10 at a position surrounding the IDT electrode 11 and the reflector 19. In addition, a wiring electrode pad 18 connected to the IDT electrode 11 through the extraction electrode 17 is formed in the surface acoustic wave element 1.

  As shown in FIG. 2 which is a cross-sectional view, the surface acoustic wave element 1 is placed by a so-called face-down method with the main surface 10a on which the IDT electrode 11 is formed facing the upper surface of a resin mounting substrate 90. For example, the annular electrode 16 is joined to the opposing annular conductor on the mounting substrate 90 via a joining material such as solder, and the wiring electrode pad 18 is joined to the opposing wiring conductor on the mounting substrate 90. These joining surfaces are joined together by reflow melting the joining material. By this reflow melting, an annular electrode part 91 in which the annular electrode 16 and the annular conductor are joined and a wiring electrode part 92 in which the wiring electrode pad 18 and the wiring conductor are joined are formed.

  In this way, the surface acoustic wave element 1 is mounted and fixed on the mounting substrate 90 and is flip-chip mounted, whereby the surface acoustic wave element 1 is electrically and mechanically connected to the mounting substrate 90. The surface wave device S is manufactured.

The piezoelectric substrate 10 is a piezoelectric material such as a 38.7 ° Y-cut-X propagation LiTaO ₃ single crystal, a 64 ° Y-cut-X propagation LiNbO ₃ single crystal, a 45 ° X cut-Z propagation LiB ₄ O ₇ single crystal, or the like. It is made of a material having properties. Thereby, the piezoelectric substrate 10 can increase the electromechanical coupling coefficient and decrease the group delay time temperature coefficient.

  The thickness of the piezoelectric substrate 10 is preferably 0.15 to 0.5 mm. When the thickness is less than 0.15 mm, the piezoelectric substrate 10 is brittle and easily damaged. Conversely, when the thickness is 0.5 mm, the material cost increases.

  As shown in FIG. 1, the IDT electrode 11 formed on the main surface 10 a of the piezoelectric substrate 10 has a pair of electrode fingers 11 a formed in a comb-teeth shape so as to mesh with each other.

  In the electrode fingers 11a, the number of electrode fingers 11a is preferably 50 to 200 per side. The width of each electrode finger 11a is 0.1 to 10 μm. The interval (pitch) between the adjacent electrode fingers 11a is 0.1 to 10 μm. The length (intersection width) with which the opposing electrode fingers 11a are engaged is 10 to 300 μm. The IDT electrode 11 has a height (thickness) of 0.1 to 0.6 μm in order to obtain the desired characteristics as a surface acoustic wave resonator or a surface acoustic wave filter.

  The IDT electrode 11 is an electrode layer made of an Al—Cu-based Al alloy or the like, as will be described later, using a thin film forming method such as a sputtering method, a vapor deposition method or a CVD method (Chemical Vapor Deposition). And a Ti-based intermediate layer.

  The metal added to Al as the Al alloy includes Cu. Further, metals such as Ti, Ta, W, Mo, and Mg may be used together with Cu or instead of Cu. Then, the IDT electrode 11 is patterned by using a photolithography method to have a predetermined shape.

  The material of the IDT electrode 11 described above can also be applied to the reflector 19 having a slit shape in which a plurality of electrode fingers are arranged in parallel.

  In FIG. 1, a ladder type surface acoustic wave filter is shown as the surface acoustic wave element 1, but it may be constituted by a DMS type surface acoustic wave resonator filter shown in FIG. 12.

  The DMS surface acoustic wave resonator filter of FIG. 12 is similar to the ladder surface acoustic wave element 1 of FIG. 1 and includes a piezoelectric substrate 10 ′ and an IDT electrode 11 ′ formed on the main surface 10a ′ of the piezoelectric substrate 10 ′. And have. These IDT electrodes 11 'are coupled to each other through a lead wiring 17'. The surface acoustic wave element 1 ′ includes a reflector 19 ′ at a position sandwiching the IDT electrode 11 ′ in the signal propagation direction (left and right direction on the paper surface) of the IDT electrode 11 ′. In the surface acoustic wave element 1 ′, an annular electrode 16 ′ is formed at a position surrounding the IDT electrode 11 ′ and the reflector 19 ′ on the main surface 10 a ′ of the piezoelectric substrate 10 ′. In addition, the surface acoustic wave element 1 ′ is provided with a wiring electrode pad 18 ′ connected to the IDT electrode 11 ′ via the lead wiring 17 ′.

  Hereinafter, the structure of the IDT electrode will be described based on the ladder-type surface acoustic wave element 1 shown in FIG. 1. However, the structure of the IDT electrode 11 ′ of the DMS surface acoustic wave resonator filter shown in FIG. Keep it.

  FIG. 3 is a cross-sectional view of the main part of the IDT electrode 11 included in the surface acoustic wave element 1 along the line BB in FIG. FIG. 4 is an enlarged cross-sectional view of one electrode finger 11 a in the IDT electrode 11.

  The surface acoustic wave element 1 includes, as an IDT electrode 11, an electrode finger 11 a in which a plurality of conductor layers are stacked on a main surface 10 a of a piezoelectric substrate 10. This electrode finger 11 a is covered with a protective film 14.

  As shown in FIG. 3, the electrode fingers 11 a are formed on a first conductor layer (hereinafter also referred to as an intermediate layer) 12 formed on the main surface 10 a of the piezoelectric substrate 10, and on the intermediate layer 12. Two conductor layers, which are a second conductor layer (hereinafter also referred to as an electrode layer) 13, are stacked.

  As shown in FIG. 3, the intermediate layer 12 and the electrode layer 13 are formed so that a cross section in a plane orthogonal to the longitudinal direction approaches the main surface 10 a of the piezoelectric substrate 10. That is, the intermediate layer 12 and the electrode layer 13 each have a trapezoidal shape in the cross section.

  Thus, even if the material for forming the protective film 14 is formed by being incident from a direction substantially perpendicular to the main surface 10a of the piezoelectric substrate 10 by a film forming method with less wraparound, the side surface of the electrode finger 11a Since the protective film 14 can be formed with a sufficient thickness, breakage and peeling of the protective film 14 can be suppressed.

The intermediate layer 12 is made of a metal material such as Ti (its thermal expansion coefficient is written as ρ ₁₂ ρ ₁₂ = 8.9 × 10 ⁻⁶ / K).

The electrode layer 13 is made of an Al alloy having a larger thermal expansion coefficient (the thermal expansion coefficient is written as ρ ₁₃ ) than that of the material forming the intermediate layer 12 (for example, Al − of ρ ₁₃ = 23.5 × 10 ⁻⁶ / K). It is made of a metal material such as Cu (Cu: 1 wt%) alloy).

  In addition, the electrode layer 13 is a metal mixed with Cu as a main component forming the electrode layer 13 together with Cu or a metal added with a metal such as Ti, Ta, W, Mo, or Mg described above instead of Cu. It can also be made of a material.

Further, as shown in FIG. 4, the electrode layer 13 and the intermediate layer 12 which are two conductor layers included in the electrode finger 11a are formed at an angle α ₁ (the angle between the side surface of the intermediate layer 12 and the main surface 10a of the piezoelectric substrate 10). For example, 65 ° is formed to be larger than an angle β ₁ (for example, 58 °) formed by the side surface of the electrode layer 13 and the main surface 10a of the piezoelectric substrate 10 (α ₁ > β ₁ ). Thereby, the stress which arises in each conductor layer of the electrode finger 11a can be disperse | distributed (it mentions later in detail).

The angle of the side surface of each conductor layer of the electrode finger 11a can be adjusted by performing etching as follows. That is, each conductor layer of the electrode finger 11a is laminated, and the shape thereof is patterned using a photolithography technique, and then formed using a dry etching method. In this dry etching method, Cl ₂ , BCl ₃ and N ₂ are used as reaction gases, and the etching conditions such as gas flow rate, pressure, applied power, and time are adjusted, so that the difference in etching rate between Ti and Al alloy can be reduced. Utilizing this, the side etching amount (the etching amount of the side surface portion of each conductor layer) is controlled. Thereby, the angles α ₁ and β ₁ of the side surfaces of the conductor layers (intermediate layer 12 and electrode layer 13) of the electrode finger 11a can be adjusted. Specifically, in order to increase the side etching amount, that is, to reduce the angle formed between the side surface of the conductor layer and the main surface of the piezoelectric substrate, increase the gas concentration of BCl ₃ and increase the applied power. Is effective.

  The protective film 14 is covered to protect the electrode finger 11a. The protective film 14 is formed by forming a predetermined material on the IDT electrode 11 using the CVD method after forming the IDT electrode 11. In addition to using the CVD method, the protective film 14 can also be formed using a method such as a sputtering method or a vapor deposition method.

  Note that the protective film 14 is a conductive protective film formed of a conductive material, a semiconductor film formed of a semiconductor material, or an insulating protective film formed of an insulating material. be able to.

  In the case of a conductor protective film, it is described here as being formed of Ti, but in addition to Ti, one of metal materials such as Cr, Nb, Pd, Cu and Ni is used as a main component. Can do. The conductor protective film 14 is formed only on the electrode finger 11 a of the IDT electrode 11.

  The insulating protective film is formed of an insulating material such as silicon dioxide or silicon nitride. The semiconductor film is formed of a semiconductor material such as polycrystalline silicon. At this time, the insulating protective film and the semiconductor film may be formed only on the electrode finger 11a, or may be formed on the main surface 10a of the piezoelectric substrate 10 in addition to the electrode finger 11a.

In the following, in the surface acoustic wave device 1, the angle alpha _1, based on the beta ₁ configuration, illustrating the mechanism of reduction of shear stress generated in the conductor layers.

In the vicinity of the side surface of each conductor layer (intermediate layer 12 and electrode layer 13), stress due to thermal expansion of each conductor layer is generated outward in a direction substantially perpendicular to the side surface of each conductor layer. As shown in FIG. 4, the thermal expansion width A ₁ is elongated near the side surface of the intermediate layer 12, and the thermal expansion width B ₁ is elongated near the side surface of the electrode layer 13. Here, “the width of thermal expansion” represents the width of extension in a direction substantially perpendicular to the side surface of each conductor layer, and is defined by the volume of the conductor layer, the width in the plane direction, the thermal expansion coefficient ρ, and the like. The

In this example, since the thermal expansion coefficient ρ ₁₂ of the intermediate layer 12 is smaller than the thermal expansion coefficient ρ ₁₃ of the electrode layer 13, the thermal expansion width A ₁ is smaller than the thermal expansion width B ₁ (A ₁ < B _1).

Therefore, in the intermediate layer 12, the expansion that occurs in the direction along the main surface 10a of the piezoelectric substrate 10 due to the thermal expansion width A1 is A ₁ sin α ₁ , and in the electrode layer 13, the piezoelectric substrate 10 has the thermal expansion width B1. Elongation occurring in the direction along the main surface 10a is B ₁ sin β ₁ .

Here, the angle α ₁ of the side surface of the intermediate layer 12 is formed larger than the angle β ₁ of the side surface of the electrode layer 13 (sin α ₁ > sin β ₁ ), so that the main surface 10 a of the piezoelectric substrate 10 in each conductor layer is formed. extension occurring in the direction along _{(a 1 sinα 1, B 1} sinβ 1) may be the side surface of each of the conductor layers compared to when it is formed at the same angle, to reduce the difference.

  Therefore, by adjusting the angle formed by the side surface of each conductor layer according to the thermal expansion coefficient of the conductor layer, it is possible to reduce the shear stress generated at the interface between the intermediate layer 12 and the electrode layer 13, As a result, breakage and peeling of the protective film 14 can be suppressed.

Incidentally, the angle α ₁ formed by the side surface of the intermediate layer 12 preferably has an angle not exceeding 80 degrees. By taking a value in a range where this angle does not exceed 80 degrees, the protective film 14 is formed on the side surface of the electrode finger 11a even when the protective film 14 is formed by using a film forming method with less wraparound, for example. It is possible to have a sufficient thickness up to a portion close to the main surface 10a, and to have good adhesion to the intermediate layer 12 and the electrode layer 13.

Further, the difference in angle (α ₁ −β ₁ ) between the intermediate layer 12 and the electrode layer 13 is preferably in the range of 10 ° to 20 °, more preferably 15 °. Thereby, at this time, the protective film 14 has good adhesion to the intermediate layer 12 and the electrode layer 13.

  Next, a surface acoustic wave device according to another embodiment of the present invention will be described. In the following description, the surface acoustic wave elements 2, 3, and 4 (including the piezoelectric substrates 20, 30, and 40, their main surfaces 20a, 30a, and 40a, and the IDT electrodes 21, 31, and 41) are not particularly referred to. 1, the surface acoustic wave device 1 (including the piezoelectric substrate 10, its main surface 10a, and IDT electrode 11) of FIG. 1 and the surface acoustic wave device 1 'of FIG. 12 (the piezoelectric substrate 10', its main surface 10a ', IDT). The electrode 11 ′ is included in the structure.

  FIG. 5 is a cross-sectional view of an essential part of the IDT electrode 21 included in the surface acoustic wave element 2 according to another embodiment, taken along line BB in FIG. 1, and FIG. It is an expanded sectional view of electrode finger 21a.

  The surface acoustic wave element 2 includes an electrode finger 21 a in which a plurality of conductor layers are stacked on the main surface 20 a of the piezoelectric substrate 20 as the IDT electrode 21. This electrode finger 21 a is covered with a protective film 24.

  As shown in FIG. 5, the electrode finger 21 a includes an intermediate layer 22 that is a first conductor layer formed on the main surface 20 a of the piezoelectric substrate 20, and a second layer formed on the intermediate layer 22. Two conductor layers are laminated with the electrode layer 23 which is a conductor layer. As shown in FIG. 5, the intermediate layer 22 and the electrode layer 23 included in the electrode finger 21 a are formed so that a cross section in a plane perpendicular to the longitudinal direction approaches the main surface 20 a of the piezoelectric substrate 20. Yes. That is, the intermediate layer 22 and the electrode layer 23 each have a trapezoidal shape in the cross section.

Intermediate layer 22, and write a Al alloy (thermal expansion coefficient containing a metal material such as Cu and Mg and [rho ₂₂ to Al, the ^{_{ρ 22 = 23.5 × 10 -6 /}} K Al-Cu (Cu: 1% by weight) and other metal materials.

The electrode layer 23 has a smaller thermal expansion coefficient ρ ₂₃ than the material forming the intermediate layer 22 (when the thermal expansion coefficient is written as ρ ₂₃ , the thermal expansion coefficient ρ ₂₃ = 6.6 × 10 ⁻⁶ / K ) Or the like.

As shown in FIG. 6, the two conductor layers forming the electrode fingers 21 a have an angle α ₂ (for example, 60 °) formed between the side surface of the intermediate layer 22 and the main surface 20 a of the piezoelectric substrate 20. And the main surface 20a of the piezoelectric substrate 20 is formed so as to be smaller than an angle β ₂ (for example, 75 °) (α ₂ <β ₂ ).

  The protective film 24 is provided to protect the electrode fingers 21a. As with the protective film 14, the protective film 24 is formed by forming a predetermined material on the IDT electrode 21 using the CVD method after forming the IDT electrode 21.

In the vicinity of the side surface of the intermediate layer 22, the expansion of the thermal expansion width A ₂ occurs, and in the vicinity of the side surface of the electrode layer 23, the expansion of the thermal expansion width B ₂ occurs. At this time, since the thermal expansion coefficient [rho ₂₂ of the intermediate layer 22 is larger than the thermal expansion coefficient [rho ₂₃ of the electrode layer 23, the width _{A 2} of thermal expansion is larger than the width _{B 2} of the thermal expansion _(A 2> _{B 2} ).

Therefore, in the intermediate layer 22, the expansion that occurs in the direction along the main surface 20 a of the piezoelectric substrate 20 due to the thermal expansion width A ₂ becomes A ₂ sin α ₂ , and in the electrode layer 23, the piezoelectric substrate 20 due to the thermal expansion width B 2. Elongation that occurs in the direction along the main surface 20a of the film becomes B ₂ sin β ₂ . Since the angle α ₂ of the side surface of the intermediate layer 22 is formed smaller than the angle β ₂ of the side surface of the electrode layer 23 (sin α ₂ <sin β ₂ ), in the direction along the main surface 20 a of the piezoelectric substrate 20 in each conductor layer. resulting elongation _{(a 2 sinα 2, B 2} sinβ 2) may be the side surface of each of the conductor layers compared to when it is formed at the same angle, to reduce the difference.

  Therefore, by adjusting the angle formed by the side surface of each conductor layer according to the thermal expansion coefficient of the conductor layer, the shear stress generated at the interface between the intermediate layer 22 and the electrode layer 23 can be reduced. As a result, breakage and peeling of the protective film 24 can be prevented.

The angle α ₂ formed by the side surface of the intermediate layer 22 is preferably an angle in the range of 45 ° to 80 °. More preferably, it is in the range of 60 ° to 80 °.

The electrode pattern of the high-frequency filter is miniaturized, and a minute mass difference on the electrode finger 21a becomes important. This mass difference means an electrode mass difference based on the shape of the electrode thin film on the piezoelectric substrate 20. Here, the shape of the IDT electrode 21, that is, the mass of the electrode finger 21a forming the IDT electrode 21, affects the excitation of the surface acoustic wave. This is called the “mass effect” and affects the frequency characteristics of surface acoustic waves, and the center frequency in these characteristics depends on the mass of the electrode thin film (particularly the line width and film thickness). May deviate from the value. If the angle angle alpha ₂ of the side surface of the intermediate layer 22 is more than 45 degrees, it is possible to reduce the mass effect of the above, the design values of the frequency characteristics differ greatly less the measured values, a stable Yield can be obtained.

Further, the difference in angle (α ₂ −β ₂ ) between the intermediate layer 22 and the electrode layer 23 is preferably in the range of 10 ° to 20 °, and more preferably 15 °. At this time, the protective film 24 has good adhesion to the intermediate layer 22 and the electrode layer 23.

  FIG. 7 is a cross-sectional view of the main part of the IDT electrode 31 included in the surface acoustic wave element 3 according to still another embodiment, taken along line BB in FIG. FIG. 8 is an enlarged cross-sectional view of one electrode finger 31 a in the IDT electrode 31.

  The surface acoustic wave element 3 includes an electrode finger 31 a in which a plurality of conductor layers are stacked on the main surface 30 a of the piezoelectric substrate 30 as the IDT electrode 31. This electrode finger 31 a is covered with a protective film 34.

  As shown in FIG. 7, the electrode finger 31 a has two conductor layers, an intermediate layer 32 formed on the main surface 30 a of the piezoelectric substrate 30 and an electrode layer 33 formed on the intermediate layer 32. Are stacked.

  As shown in FIG. 7, the intermediate layer 32 and the electrode layer 33 included in the electrode finger 31 a are formed so that a cross section in a plane perpendicular to the longitudinal direction approaches the main surface 30 a of the piezoelectric substrate 30. Yes. That is, the intermediate layer 32 and the electrode layer 33 each have a trapezoidal shape in the cross section.

  The lower surface of the electrode layer 33 in the electrode finger 31a, that is, the bonding surface 33a with the intermediate layer 32 is included in the bonding surface 32a of the intermediate layer 32 without protruding from the bonding surface 32a of the intermediate layer 32.

  The width L1 of the cross section of the bonding surface 32a where the intermediate layer 32 faces the electrode layer 33 is equal to the width L2 of the cross section of the bonding surface 33a where the electrode layer 33 faces the intermediate layer 32, as shown in FIG. It is formed to be larger than that.

  Therefore, the electrode finger 31a has an L-shaped vertical cross section as a region where the protective film 34 can be formed directly on the bonding surface 32a of the intermediate layer 32 between the side surface of the intermediate layer 32 and the side surface of the electrode layer 33. And it has the step part 32b which has width | variety R3 on either side. In the stepped portion 32b, the protective film 34 is formed directly on the bonding surface 32a of the intermediate layer 32. For example, when the electrode fingers are etched, such a stepped portion is overetched by extending the etching time so that the intermediate layer has a width L1 of the cross section of the joint surface facing the electrode layer. Can be made longer than the width L2 of the cross section of the joint surface where the electrode layer faces the intermediate layer.

Intermediate layer 32, Ti (Writing the thermal expansion coefficient and _{ρ 32, ρ 32 = 8.9 ×} 10 -6 / K) is formed of a metallic material such as.

Electrode layer 33, when the Al alloy (thermal expansion coefficient having an intermediate layer 32 larger thermal expansion coefficient [rho ₃₃ than the material forming the write and [rho _33, the ^{_{ρ 33 = 23.5 × 10 -6 /}} K Al -Cu (Cu: 1% by weight) alloy) or the like.

As shown in FIG. 8, the two conductor layers forming the electrode finger 31 a have an angle α ₃ (for example, 65 °) formed between the side surface of the intermediate layer 32 and the main surface 30 a of the piezoelectric substrate 30, as shown in FIG. And the main surface 30a of the piezoelectric substrate 30 are formed to be larger than an angle β ₃ (for example, 58 °) (α ₃ > β ₃ ).

As described above, since the angle α ₃ of the side surface of the intermediate layer 32 is formed larger than the angle β ₃ of the side surface of the electrode layer 33, the shear stress generated in the electrode finger 31a is the same angle as the side surface of each conductor layer. The difference can be reduced as compared with the case where it is formed.

  As a result, the shear stress generated at the interface between the intermediate layer 32 and the electrode layer 33 can be reduced by adjusting the angle formed by the side surfaces of each conductor layer according to the thermal expansion coefficient of the conductor layer. As a result, breakage and peeling of the protective film 34 can be prevented.

  The protective film 34 has a smaller thermal expansion coefficient than the largest thermal expansion coefficient (in this case, ρ33) of the thermal expansion coefficients ρ32 and ρ33 of each conductor layer (intermediate layer 32 and electrode layer 33) forming the IDT electrode 31. It is formed with the material which has. Thereby, the expansion | extension by the thermal expansion of the electrode layer 33 is suppressed by the protective film 34 on the step part 32b. Therefore, the shear stress generated at the boundary between the intermediate layer 32 and the electrode layer 33 can be further suppressed. In addition, the adhesion of the protective film 34 can be improved.

  FIG. 9 is a cross-sectional view of a principal part taken along line BB in FIG. 1 of an IDT electrode 41 according to still another embodiment. FIG. 10 is an enlarged cross-sectional view of one electrode finger 41 a in the IDT electrode 41.

  The surface acoustic wave element 4 includes, as an IDT electrode 41, an electrode finger 41a in which a plurality of conductor layers are stacked on the main surface 40a of the piezoelectric substrate 40. The electrode finger 41 a is covered with a protective film 44.

  As shown in FIG. 9, the electrode finger 41 a has two conductor layers, an intermediate layer 42 formed on the main surface 40 a of the piezoelectric substrate 40 and an electrode layer 43 formed on the intermediate layer 42. However, a total of four layers are laminated alternately.

  The intermediate layer 42 and the electrode layer 43 included in the electrode finger 41 a are formed so that a cross section in a plane perpendicular to the longitudinal direction thereof becomes closer to the main surface 40 a of the piezoelectric substrate 40. That is, the intermediate layer 42 and the electrode layer 43 each have a trapezoidal shape.

  As shown in FIG. 10, the width of the cross section of the bonding surface 42a where the intermediate layer 42 of the electrode finger 41a faces the electrode layer 43 is equal to the width of the cross section of the bonding surface 43a of the electrode layer 43 facing the intermediate layer 42. It is formed larger than the width. Therefore, the electrode finger 41a has an L-shaped vertical cross section as a region where the protective film 44 can be directly formed on the bonding surface 42a of the intermediate layer 42 between the side surface of the intermediate layer 42 and the side surface of the electrode layer 43. A step portion 42b having a shape and a width R4 is provided on the left and right. For example, when the electrode fingers are etched, such a stepped portion is formed by extending the etching time and performing over-etching, thereby reducing the width of the cross section of the joint surface where the intermediate layer faces the electrode layer. The electrode layer can be longer than the width of the cross section of the joint surface facing the intermediate layer.

Intermediate layer 42, Ti (Writing the thermal expansion coefficient and _{ρ 42, ρ 42 = 8.9 ×} 10 -6 / K) is formed of a metallic material such as.

Electrode layer 43, when the Al alloy (thermal expansion coefficient having a large thermal expansion coefficient than the material forming the intermediate layer 42 and writing [rho _43, the ^{_{ρ 43 = 23.5 × 10 -6 /}} K Al-Cu (Cu: 1 wt%) alloy) or the like.

As shown in FIG. 10, the plurality of conductor layers forming the electrode fingers 41 a are such that the angle α ₄ (for example, 74 °) formed between the side surface of the intermediate layer 42 and the main surface 40 a of the piezoelectric substrate 40 is the side surface of the electrode layer 43. And the main surface 40a of the piezoelectric substrate 40 are formed to be larger than an angle β ₄ (for example, 60 °) (α ₄ > β ₄ ).

The protective film 44 is made of a material having a thermal expansion coefficient smaller than the largest thermal expansion coefficient (in this case, ρ ₄₃ ) of the thermal expansion coefficients ρ ₄₂ and ρ ₄₃ of the conductor layers 42 and 43 forming the IDT electrode 41. Is formed.

Shear stress generated in the electrode finger 41a, as described above, since the intermediate layer 42 side of the angle alpha ₄ of is larger than the side surface of the angle beta ₄ of the electrode layer 43, the side surface is the same angle of the conductor layers The difference can be reduced as compared with the case where it is formed. In addition, since the width of the cross section of the bonding surface 43a of the electrode layer 43 is smaller than the width of the cross section of the bonding surface 42a of the intermediate layer 42, the protective film 44 stacked on the step portion 42b is The elongation due to the thermal expansion of the electrode layer 43 can be suppressed. Thereby, the shear stress which arises in the boundary of the intermediate | middle layer 42 and the electrode layer 43 can be reduced, and the fracture | rupture and peeling of the protective film 44 can be prevented as a result.

  Further, in the stepped portion 42b, the protective film 44 is formed directly on the bonding surface 42a of the intermediate layer 42. Therefore, the main surface of the piezoelectric substrate 40 of the electrode layer 43 having a larger thermal expansion coefficient ρ43 than the intermediate layer 42. Expansion in the 40a direction can be suppressed.

  In the present embodiment, since the electrode finger 41a is formed of three or more conductor layers, the durability of the electrode finger 41a can be further increased.

  In the above-described surface acoustic wave element 1, the embodiment in which the conductor protective film is formed only on the IDT electrode has been described. However, as shown in FIG. 11, the insulating protection is further provided on the upper surface of the conductor protective film of the electrode finger 11a. The film 14b can be formed, or the insulating protective film 14b can be formed instead of the conductor protective film. Thereby, the adhesion between the electrode finger 11a and the piezoelectric substrate 10 can be enhanced while protecting the IDT electrode 11. When forming the insulating protective film 14 b, the insulating protective film 14 b may be formed also on the main surface of the piezoelectric substrate 10. Of course, in the surface acoustic wave elements 2, 3, and 4, an insulating protective film can be similarly formed on the IDT electrodes 21, 31, and 41.

<Example 1>
The surface acoustic wave device 1 shown in FIGS. 3 and 4 was manufactured. As the piezoelectric substrate 10, a substrate formed of LiTaO ₃ single crystal was used as a material having piezoelectricity.

  A sputtering method is used to deposit Ti as an intermediate layer 12 on the piezoelectric substrate 10, and an Al—Cu (Cu: 1 wt%) alloy containing Cu in Al as an electrode layer 13 on the intermediate layer 12. Deposited. The film thickness was 18 nm for Ti and 402 nm for Al—Cu alloy.

  The IDT electrode 11 and the reflector 19 were formed by patterning their shapes using a photolithographic technique and then using a dry etching method.

In the dry etching method, Cl ₂ , BCl ₃ and N ₂ were used as reaction gases, and the etching selectivity of Ti and Al—Cu alloy was adjusted by adjusting the etching conditions such as gas flow rate, pressure and applied power. .

That is, by adjusting the etching conditions such as gas flow rate, pressure, applied power, time, etc., the tilt angles α ₁ and β ₁ are adjusted by controlling the side etching amount according to the difference in etching rate between Ti and Al—Cu alloy. did. Specifically, the RIE apparatus used is an ICP (Inductive Coupled Plasma) -RIE apparatus, and the etching conditions are such that the gas flow rate BCl3 is 20 sccm, Cl2 is 20 sccm, N2 is 10 sccm, the pressure is 1.0 Pa, and the bias power is 60 W. The etching time required for processing is about 60 seconds.

Angle of the side surface of the electrode fingers 11a at this time, when referenced to the principal surface 10a of the piezoelectric substrate 10, an angle alpha ₁ having the intermediate layer 12 is 65 degrees, the angle beta ₁ with the side surface of the electrode layer 13 is 58 degrees Met.

  Next, after forming the intermediate layer 12 and the electrode layer 13, the metal layer (Ti) used as the protective film 14 was formed by sputtering method using the mask used at the time of dry etching.

  Even when a high frequency was applied to the surface acoustic wave element 1 thus manufactured and the environmental temperature was changed, the protective film 14 did not peel off. Further, a high yield was obtained in the wafer surface and between the wafers of the surface acoustic wave element 1.

<Example 2>
The surface acoustic wave element 2 shown in FIGS. 5 and 6 was manufactured. As the piezoelectric substrate 20, a substrate made of LiTaO ₃ single crystal was used as a piezoelectric material.

  First, an Al—Cu (Cu: 1 wt%) alloy was deposited as the intermediate layer 22 on the piezoelectric substrate 20 by sputtering, and Ti was deposited as the electrode layer 23 on the intermediate layer 22. The film thickness was 402 nm for Al—Cu and 18 nm for Al—Cu alloy.

The IDT electrode 21 and the reflector (not shown) are formed by patterning their shapes using a photolithographic technique and then using a dry etching method. At this time, etching of the intermediate layer 22 and the electrode layer 23 is performed. The selectivity was adjusted. Further, by using this dry etching method, the angle formed between the side surface of each conductor layer included in the electrode finger 21a and the main surface 20a of the piezoelectric substrate 20 was adjusted to the designed angle. The etching conditions are such that the gas flow rate BCl ₃ is 20 sccm, Cl ₂ is 20 sccm, N ₂ is 20 sccm, the pressure is 1.0 Pa, the bias power is 60 W, and the etching time required for processing is about 60 seconds.

At this time, the angle of the side surface of the electrode fingers 21a, when relative to the main surface 20a of the piezoelectric substrate 20, an angle alpha ₂ having the intermediate layer 22 is 60 degrees, the angle beta ₂ with the side surface of the electrode layer 23 is 75 degrees Met.

Next, after the intermediate layer 22 and the electrode layer 23 were formed, the protective film 24 was formed of SiO ₂ using a sputtering method. Then, unnecessary portions of the protective film 34 were removed by dry etching.

  Even when a high frequency was applied to the surface acoustic wave element 2 thus manufactured and the environmental temperature was changed, the protective film 24 was not peeled off.

<Example 3>
The surface acoustic wave element 3 shown in FIGS. 7 and 8 was manufactured. As the piezoelectric substrate 30, a substrate formed of LiTaO ₃ single crystal was used as a piezoelectric material.

  Next, Ti was deposited as an intermediate layer 32 on the piezoelectric substrate 30 by sputtering, and an Al—Cu (Cu: 1 wt%) alloy was deposited as an electrode layer 33 on the intermediate layer 32. The film thickness was 18 nm for Ti and 402 nm for Al—Cu alloy.

The IDT electrode 31 and the reflector (not shown) were formed by patterning their shapes using a photolithographic technique and then using a dry etching method. In the dry etching method, Cl ₂ , BCl ₃ and N ₂ were used as reaction gases, and the etching selectivity of the intermediate layer 32 and the electrode layer 33 was adjusted by adjusting the etching conditions such as gas flow rate, pressure and applied power. . Further, by using this dry etching method, the angle formed between the side surface of each conductor layer included in the electrode finger 31a and the main surface 30a of the piezoelectric substrate 30 was adjusted to the designed angle. The etching conditions are such that the gas flow rate BCl ₃ is 20 sccm, Cl ₂ is 20 sccm, N ₂ is 10 sccm, the pressure is 1.0 Pa, the bias power is 60 W, and the etching time required for the processing is about 70 seconds.

At this time, the angle of the side surface of the electrode fingers 31a, when referenced to the principal surface 30a of the piezoelectric substrate 30, the angle alpha ₃ with the intermediate layer 32 is 65 degrees, the angle beta ₃ with the side surface of the electrode layer 33 is 58 degrees Met.

  Further, by performing over-etching when the electrode finger 31a is etched, the width of the cross section of the bonding surface 33a of the electrode layer 33 is shorter by 8 nm each on the left and right than the width of the cross section of the bonding surface 32a of the intermediate layer 32. (See R3 in FIG. 8).

Next, after forming the intermediate layer 32 and the electrode layer 33, patterning was performed by photolithography, and the protective film 34 was formed of SiO ₂ by sputtering. Then, unnecessary portions of the protective film 34 were removed by dry etching.

  Even when a high frequency was applied to the surface acoustic wave element 3 thus produced and the environmental temperature was changed, the protective film 34 did not peel off.

<Example 4>
The surface acoustic wave element 4 shown in FIGS. 9 and 10 was manufactured. As the piezoelectric substrate 40, a substrate made of LiTaO ₃ single crystal was used as a piezoelectric material.

  First, Ti serving as the intermediate layer 42 was deposited on the piezoelectric substrate 40 by sputtering, and an Al—Cu (Cu: 1 wt%) alloy serving as the electrode layer 43 was deposited on the intermediate layer 42. In this way, the intermediate layer 42 and the electrode layer 43 were alternately stacked on the main surface 40 a of the piezoelectric substrate 40. The film thickness was 6 nm for Ti per layer and 130 nm for Al—Cu alloy.

The IDT electrode 41 and the reflector (not shown) were formed by patterning their shapes using a photolithographic technique and then using a dry etching method. In the dry etching method, Cl ₂ , BCl _3, and N ₂ were used as reaction gases, and the etching selectivity of the intermediate layer 42 and the electrode layer 43 was adjusted by adjusting etching conditions such as gas flow rate, pressure, and applied power. . Further, by using this dry etching method, the angle formed between the side surface of each conductor layer included in the electrode finger 41a and the main surface 40a of the piezoelectric substrate 40 was adjusted to the designed angle. The etching conditions are such that the gas flow rate BCl ₃ is 20 sccm, Cl ₂ is 20 sccm, N ₂ is 10 sccm, the pressure is 1.0 Pa, the bias power is 60 W, and the etching time required for processing is about 60 seconds.

At this time, the angle of the side surface of the electrode fingers 41a, when referenced to the principal surface 40a of the piezoelectric substrate 40, the angle alpha ₄ with the intermediate layer 42 is 74 degrees, the angle beta ₄ with the side surface of the electrode layer 43 is 60 degrees Met.

  Further, by performing over-etching when the electrode finger 41a is etched, the width of the cross section of the joint surface 42a of the intermediate layer 42 is 16 nm longer than the width of the cross section of the joint surface 43a of the electrode layer 43. (See R4 in FIG. 10).

Next, after forming the intermediate layer 42 and the electrode layer 43, patterning was performed by photolithography, and the protective film 44 was formed of SiO ₂ by sputtering. And after forming the protective film 44, the IDT electrode 41 was formed by the dry etching method.

  Even when a high frequency was applied to the surface acoustic wave element 4 thus manufactured and the environmental temperature was changed, the protective film 44 did not peel off.

1 is a plan view of a surface acoustic wave element according to an embodiment of the present invention. It is sectional drawing in the AA line which shows the state which mounted the surface acoustic wave element in the mounting board | substrate. FIG. 3 is a cross-sectional view of the main part of the IDT electrode included in the surface acoustic wave element 1 along the line BB in FIG. 1. It is an expanded sectional view of one electrode finger in this IDT electrode. It is principal part sectional drawing in the BB line in FIG. 1 of the IDT electrode contained in the surface acoustic wave element 2 concerning other embodiment. It is an expanded sectional view of one electrode finger in this IDT electrode. It is principal part sectional drawing in the BB line in FIG. 1 of the IDT electrode contained in the surface acoustic wave element 3 concerning further another embodiment. It is an expanded sectional view of one electrode finger in this IDT electrode. It is principal part sectional drawing in the BB line in FIG. 1 of the IDT electrode contained in the surface acoustic wave element 4 concerning further another embodiment. It is an expanded sectional view of one electrode finger in this IDT electrode. 3 is an enlarged cross-sectional view showing a state in which an insulating protective film is formed on electrode fingers of IDT electrodes included in the surface acoustic wave element 1. FIG. It is a top view of the surface acoustic wave element concerning other embodiments of the present invention. It is an expanded sectional view of the electrode finger of the conventional IDT electrode.

Explanation of symbols

1, 2, 3, 4 Surface acoustic wave elements 10, 20, 30, 40 Piezoelectric substrates 10a, 20a, 30a, 40a Main surfaces 11, 21, 31, 41 of piezoelectric substrates IDT electrodes 11a, 21a, 31a, 41a Electrode fingers 12, 22, 32, 42 Intermediate layers 13, 23, 33, 43 Electrode layers 14, 24, 34, 44 Protective film 14b Insulating protective film

Claims (11)

A piezoelectric substrate;
An IDT electrode formed on the main surface of the piezoelectric substrate and having electrode fingers;
The electrode finger is formed by laminating a plurality of conductor layers including a first conductor layer and a second conductor layer made of a material different from the material of the first conductor layer,
The first conductor layer has a trapezoidal shape in which a cross-sectional shape in a plane orthogonal to the longitudinal direction of the electrode fingers extends in a direction approaching the piezoelectric substrate,
The second conductor layer has a trapezoidal shape in which a cross-sectional shape in a plane orthogonal to the longitudinal direction of the electrode fingers extends in a direction approaching the piezoelectric substrate,
The surface acoustic wave element, wherein an angle formed between a side surface of the first conductor layer and a main surface of the piezoelectric substrate is different from an angle formed between a side surface of the second conductor layer and the main surface of the piezoelectric substrate.   2. The surface acoustic wave device according to claim 1, wherein a thermal expansion coefficient of a material of the first conductor layer of the electrode finger is different from a thermal expansion coefficient of a material of the second conductor layer. The second conductor layer is formed of a material having a larger thermal expansion coefficient than the first conductor layer,
The angle formed between the side surface of the first conductor layer and the main surface of the piezoelectric substrate is larger than the angle formed between the side surface of the second conductor layer and the main surface of the piezoelectric substrate. 2. The surface acoustic wave device according to 2. The second conductor layer is formed of a material having a smaller coefficient of thermal expansion than the first conductor layer,
The angle formed between the side surface of the first conductor layer and the main surface of the piezoelectric substrate is smaller than the angle formed between the side surface of the second conductor layer and the main surface of the piezoelectric substrate. 2. The surface acoustic wave device according to 2. The first conductor layer is formed on and in contact with the main surface of the piezoelectric substrate,
The second conductor layer is formed on the first conductor layer;
A width of a section of the first conductor layer facing the second conductor layer is formed larger than a width of a section of the second conductor layer facing the first conductor layer. The surface acoustic wave device according to any one of claims 1 to 4, wherein the surface acoustic wave device is provided. The first conductor layer is formed on and in contact with the main surface of the piezoelectric substrate,
The second conductor layer is formed on the first conductor layer;
A third conductor layer formed of the same material as the first conductor layer is formed on the second conductor layer;
A fourth conductor layer formed of the same material as the second conductor layer is formed on the third conductor layer;
The angle formed between the side surface of the third conductor layer and the main surface of the piezoelectric substrate is formed to be the same as the angle formed between the side surface of the first conductor layer and the main surface of the piezoelectric substrate,
The angle formed between the side surface of the fourth conductor layer and the main surface of the piezoelectric substrate is formed to be the same as the angle formed between the side surface of the second conductor layer and the main surface of the piezoelectric substrate. The surface acoustic wave element according to any one of claims 1 to 4.   The surface acoustic wave device according to any one of claims 1 to 6, wherein a cross-sectional shape of the first conductor layer and a cross-sectional shape of the second conductor layer are formed by a dry etching method.   The surface acoustic wave device according to claim 1, wherein the electrode finger of the IDT electrode is covered with a protective film.   The surface acoustic wave according to claim 8, wherein the protective film is made of a material having a smaller thermal expansion coefficient than that of the conductor layer forming the electrode finger having the largest thermal expansion coefficient. element. The protective film is formed on the IDT electrode,
The surface acoustic wave device according to claim 8 or 9, comprising at least one of Ti, Cr, Nb, Pd, Cu, and Ni as a material.   A surface acoustic wave device in which the surface acoustic wave element according to claim 1 is mounted on a mounting substrate.

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